Conventionally, in order to obtain low on-resistance while obtaining a high breakdown voltage, a semiconductor device in the related art is formed using a semiconductor substrate having a super junction structure with a PN column structure formed by repetitively placing a P-type region and an N-type region in a planar direction.
As a manufacturing method of the semiconductor substrate as above, for example, PTL 1 proposes a method as follows. Firstly, in a semiconductor wafer having a plurality of chip forming regions, trenches are formed in the respective chip forming regions. Thereafter, trenches with a desired depth are formed by repetitively performing respective steps: a protection film forming step of forming a protection film on a wall surface of each trench by turning a C4F8 gas into plasma, an evacuation step of evacuating the C4F8 gas, and an etching step of digging down the trench by removing the protection film formed on a bottom surface of the trench by turning an SF6 gas into plasma.
According to the proposed method above, a semiconductor substrate with a PN column structure is manufactured by embedding an epitaxial film in each trench. By dividing the semiconductor substrate into chips after a typical semiconductor fabrication process is performed, a semiconductor device having a PN column structure is manufactured.
Because the C4F8 gas is evacuated after the protection film is formed, mixing of the C4F8 gas with the SF6 gas at the etching process can be suppressed. Accordingly, a reduction in strength of the protection film at the etching process can be suppressed and hence application of damage on the semiconductor wafer can be suppressed.